The enzymology and regulation of adrenal cortex steroidogenesis will be studied, with emphasis on the rate-limiting, ACTH- regulated side-chain cleavage of cholesterol. The rate of this mitochondrial reaction is determined by both the enzyme system, cytochrome P-450 side chain cleavage, and the intramitochondrial delivery of cholesterol to the enzyme. The latter appears to utilize a regulated transporter which moves cholesterol from the outer to the inner membrane. Studies include a characterization of the transporter, elucidation of cholesterol pools within the mitochondrion, and modulation of adrenal function by the immune system. Technique include measurement of cytochrome P-450 spin state using uv-visible spectrophotometry; radio-immunoassay; gas chromatography; HPLC; and tissue culture.